The French-British-American (FAB) Cooperative Group has classified chronic T-lymphoid leukemias into four subgroups: (i) T-cell or LGL leukemia, (ii) T-prolymphocytic leukemia (T-PLL), (iii) adult T-cell leukemia/lymphoma, and (iv) Sezary's syndrome (Bennett, et al., 1989).
Chronic lymphocytic leukemia (CLL) of T-cell origin was first identified in 1975. In many patients the abnormal cells were large granular lymphocytes (LGL) (Brouet, et al., 1975). The MIC Cooperative Group reviewed the FAB classification in 1990 and proposed that Large Granular Lymphocyte (LGL) leukemia should replace T-CLL as the preferable terminology (Bennett, et al., 1990).
Clonal disorders of LGL may arise from either natural killer cells or T cells; it has been suggested that these diseases be designated, NK-and T-LGL leukemia, respectively (Loughran, 1993). T-LGL leukemia is characterized by clonal proliferation of CD3+ LGL with are usually also CD8+, CD16+, and CD57+ (Loughran, 1993; Loughran, et al., 1985; Loughran and Starkebaum, 1987; Newland, et al., 1984; Semenzato, et al., 1987).
Clinical manifestations of T-LGL leukemia include rheumatoid arthritis, splenomegaly, and hematologic abnormalities such as chronic or cyclic neutropenic, autoimmune thrombocytopenia, and pure red cell aplasia (Loughran, 1993; Loughran, et al., 1985; Loughran and Starkebaum, 1987; Newland, et al., 1984; Semenzato, et al., 1987; Loughran and Hammond, 1988).